The field of application of the invention lies in particular in gas turbine aeroengines. Nevertheless, the invention is applicable to other turbine engines, for example industrial turbines.
Ceramic matrix composite (CMC) materials are known for conserving their mechanical properties at high temperatures, which makes them suitable for constituting hot structural elements.
In gas turbine aeroengines, both improving efficiency and also reducing certain polluting emissions lead to seeking operation at ever higher temperatures. For turbine ring assemblies that are made entirely out of metal, it is necessary to cool all of the elements of the assembly, and in particular the turbine ring, which is subjected to very hot streams, typically at temperatures higher than can be withstood by the metal material. Such cooling has a significant impact on the performance of the engine since the cooling stream that is used is taken from the main stream through the engine. In addition, the use of metal for the turbine ring limits the potential for increasing temperature in the turbine, even though such an increase would make it possible to improve the performance of aeroengines.
Furthermore, a metal turbine ring assembly deforms under the effect of high temperature streams, thereby modifying clearances in the flow passage and consequently modifying the performance of the turbine.
That is why using CMCs for various hot parts of engines has already been envisaged, particularly since CMCs present the additional advantage of density that is lower than the density of the refractory metals traditionally used.
Thus, making turbine ring sectors as single pieces out of CMC is described in particular in Document US 2012/0027572. Each ring sector comprises an annular base having an inside face that defines the inside face of the turbine ring and an outside face from which there extend two tab-forming portions, with the ends of the tabs being engaged in housings in a metal ring support structure.
The use of CMC ring sectors makes it possible to reduce significantly the amount of ventilation that is needed for cooling the turbine ring. Nevertheless, keeping the ring sectors in position remains a problem, in particular in the face of the differential expansions that can occur between the metal support structure and the ring sectors made of CMC. Specifically, during expansion of the metal support structure, it is important to ensure that the structure does not impose movements or forces on the CMC ring sectors that are too great, since which would run the risk of damaging them. That is why it is necessary to make provision for some minimum amount of clearance between the assembled-together parts. Unfortunately, such clearance means that it is not possible to have good control over the shape of the flow passage nor good behavior of the ring sectors in the event of making contact with the tips of the turbine blades. Furthermore, the presence of such clearance gives rise to problems of vibration.